Stakeholder Engagement

In January 2017, the City reached out to over 40 stakeholders through focus groups and interviews to understand their questions and concerns, and develop a stakeholder engagement process for WHP Zone delineation. In April, the City convened a Sounding Board of diverse perspectives to share information and seek feedback on recommended actions. The Sounding Board will meet five times through August. The City will work with Sounding Board members to develop a community level of risk tolerance for wellhead protection. The groundwater model results will provide information to aid in developing Wellhead Protection Zone revisions, ultimately resulting in proposed zone changes by the end of 2017.

Stakeholder engagement process

The City strives to provide a level of service that reflects the community’s priorities. The level of service provided is inversely related to the level of acceptable risk. Well pumping rates, recharge changes due to climate change, and effective porosity are model dials that have uncertainty and significant impacts on model results. Stakeholders will provide input on these dials to inform final zone delineation model results. Policy dials will result in buffers applied to final model results.

Community risk tolerance within the zone delineation process

Model Dials

Pumping Rates

Effective Porosity

Climate Change

Level of Service

Proactive

Risk Tolerance

Low

Pump at full water right year-round plus 10%

0.15

Use 50-year projections in climate models that predict greater impact in recharge

Reactive

High

Pump at full water right June – Sept, estimate non-peakseason pumping based on modest growth

Once the community’s risk tolerance has been identified and the model dials adjusted, the City will produce a new delineation of the WHP zones. Below are the current (left map) and preliminary (right map) WHP Zones, which will be adjusted after the risk tolerance has been considered. The preliminary zones are based on December 2016 data. Stakeholders will provide input for pumping rates, effective porosity and climate change to develop model results. Once these dials are adjusted, buffers will be evaluated and applied to model results.

Preliminary model results

The maps here show the current wellhead protection zones and the proposed new protection areas, renamed Critical Aquifer Recharge Areas. The new areas were informed by the model and developed in collaboration with stakeholders on the Wellhead Protection Sounding Board.

The modeling process first identified areas from which each City supply well captures groundwater during various groundwater times of travel.

Input from stakeholders then helped finalize risk-related assumptions within the model.

Artificial impacts to groundwater flow were analyzed to identify accessory buffers, such as Temporary Construction Dewatering (TCD). TCD is when large-scale construction projects temporarily pump groundwater away from their excavations.

The model was then used in conjunction with a groundwater vulnerability assessment to develop the updated protection areas, renamed as Critical Aquifer Recharge Areas (CARAs).

CARA #1 represents critical recharge area of the 6-mo, 1-year and 5-year groundwater capture zones, including areas affected by TCD.

CARA #2 represents groundwater capture zones beyond 5-years and within 10-years as well as areas outside the 10-year capture zone that have a critical recharging effect on the drinking water aquifer.